The present invention relates to target and relative positional change sensing. Particularly, the invention relates to monopulse systems having multiple antenna feeds and one or more signal sources.
Problems exist with known monopulse radar systems. Large numbers of parts are required. Each part increases cost of production, size and weight of the system and requires increased power and fuel in a vehicle. Each added part increases possibilities of malfunction in use or errors in assembly. An increased number of parts requires increased power and produces increased heat, which may adversely affect other parts or devices and which may adversely affect vehicle size, range or operational characteristics.
In the past, radars which have been built have been blind to one sense of polarization or another in the return signal. As a consequence, any target which is strongly polarized has the potential of being invisible, regardless of its amplitude. Even if a target has a strong reflection coefficient, if the target happens to be predominantly odd bounce, even bounce or linear, there exists a good possibility that a radar cannot see it.
Dual polarized systems have been touted primarily because of their properties regarding signal to clutter enhancement or improved target classification and identification. Dual polarization processing antennae systems receive dual polarization on their sum channels. Most have single polarization on their difference channels. If the target return is strongly polarized in one sense which is orthogonal to the difference channel polarization, the target cannot be tracked even though detected unless the transmitter can be switched from one sum channel to the orthogonally polarized sum channel. The unattractive alternatives are to provide two additional receiver channels for difference patterns or to switch two receivers between orthogonally polarized difference channels.
There has arisen in conjunction with dual polarized technology a requirement to track a target regardless of its polarization characteristic. That requirement may be referred to as a universal tracking requirement. Universal tracking capability cannot be provided even by the most sophisticated of singly polarized radars, nor is it present in any radar which transmits a single polarization and receives a single polarization. It does not matter whether such radars are co-polar or cross-polar. For any such radar, a return signal which is orthogonal to the polarization of the tracking channels cannot be seen at all. Only in a dual polarized, polarization diverse system can this be achieved.
A monopulse system is desirable for tracking applications because of performance. Reasons for using any other tracking system lie in the domain of practicality. If a monopulse system can be provided as inexpensively and as low in risk as an alternative system, a monopulse system is preferable.
The present invention provides a reduction of parts in monopulse systems in an unobvious manner to lower costs and lower risks. As a result of the present invention, other tracking systems can be disregarded for most system applications.